Hydrogenolysis of 5-carbon sugars, sugar alcohols, and methods of making propylene glycol

ABSTRACT

Methods and compositions for reactions of hydrogen over a Re-containing catalyst with compositions containing a 5-carbon sugar, sugar alcohol, or lactic acid are described. It has been surprisingly discovered that reaction with hydrogen over a Re-containing multimetallic catalyst resulted in superior conversion and selectivity to desired products such as propylene glycol. A process for the synthesis of PG from lactate or lactic acid is also described.

STATEMENT OF GOVERNMENT RIGHTS

[0001] This invention was made with Government support under contractDE-AC0676RLO 1830 awarded by the U.S. Department of Energy. TheGovernment has certain rights in this invention.

FIELD OF THE INVENTION

[0002] The present invention relates to methods and compositions forhydrogenolysis of 5 carbon sugars and sugar alcohols and hydrogenationof lactic acid.

BACKGROUND OF THE INVENTION

[0003] Currently, many of the chemicals in common use are derived frompetroleum feedstocks. However, petroleum is present in limitedunderground reserves, and the extraction, transportation, and refiningof petroleum can have severe environmental consequences.

[0004] Bio-based feedstocks, on the other hand, can be obtained fromplants and can be processed by biological processes such asfermentation. To more fully utilize bio-based materials, it is oftennecessary to convert the fermentation products or other bio-basedfeedstocks into other chemicals that can be used in a variety ofprocesses and products. Thus, it is an object of the present inventionto provide new methods of converting sugars, sugar alcohols and othersmall molecules into a variety of desired chemical products.

[0005] For a long time, scientists and engineers have sought to convertsugars and sugar alcohols into other chemical products. For example,Conradin et al. in U.S. Pat. No. 2,852,270 (filed in 1957) reported thatfor increased production of propylene glycol, hydrogenolysis should beconducted over a Ni/Cu catalyst on a carrier such as magnesium oxide.

[0006] In U.S. Pat. No. 3,030,429 (filed in 1959), Conradin et al.stated that hydrogen splitting of saccharose to glycerol and glycols canbe carried out in the presence of practically any technically feasiblecatalyst, provided that sufficient alkali is added to ensure a pH of 11to 12.5. In one example, it was reported that hydrogenolysis of anaqueous saccharose solution over a nickel-on-kieselguhr catalystproceeded with an 83% conversion to a product containing 43% glyceroland 25% propylene glycol.

[0007] Sirkar in U.S. Pat. No. 4,338,472 (filed in 1981) reportedsorbitol hydrogenolysis to produce glycerol over a nickel-on-kieselguhrcatalyst in which an alkali promoter was added to the feedstream tocontrol pH and prevent leaching of nickel from the catalyst.

[0008] Tanikella in U.S. Pat. No. 4,404,411 (filed in 1983) describedthe hydrolysis of sorbitol and xylitol in nonaqueous solvents containingat least 10 mole % base. The catalyst used in the examples was nickel onsilica/alumina. Distribution of ethylene glycol, propylene glycol andglycerol were reported.

[0009] Gubitosa et al. in U.S. Pat. No. 5,600,028 (filed in 1995)discussed the hydrogenolysis of polyhydric alcohols, such as sorbitol,over a ruthenium-on-carbon catalyst. In the examples, Gubitosa et al.reported that 100% of the sorbitol can be converted, with 41 to 51% ofthe product carbon atoms in propylene glycol.

[0010] Despite these and other efforts, there remains a need for newmethods of converting sugars and sugar alcohols to smaller moleculesthat have a variety of uses. There is also a need for novel methods ofconverting molecules such as xylitol and lactic acid into higher valueproducts such as propylene glycol and 1,3-propanediol. There isespecially a need for new methods of such conversions that providebetter yield and more desirable product distributions.

SUMMARY OF THE INVENTION

[0011] The invention provides a method of hydrogenolysis of anoxygen-containing organic compound, comprising: reacting an aqueousoxygen-containing organic compound with hydrogen at a temperature of atleast 120° C., and in the presence of a solid catalyst; where the solidcatalyst comprises a Re-containing multimetallic catalyst, and wherethere is at least 25% as much C—O hydrogenolysis occurs as C—Chydrogenolysis. In some preferred embodiments, at least 100% as much C—Ohydrogenolysis occurs as C—C hydrogenolysis. In some preferredembodiments, these percentages (such as 25%) refer to the total amountof hydrogenolysis, in other embodiments, they refer to rates, forexample, the rate of C—O hydrogenolysis is at least 25% as fast as therate of C—C hydrogenolysis. It has been surprisingly discovered that aNi/Re catalyst is superior to other catalysts.

[0012] The present invention also provides a hydrogenolysis method inwhich a 6 carbon sugar, a 6 carbon sugar alcohol, or glycerol is reactedwith hydrogen, at a temperature of at least 120 ° C., and in thepresence of a solid catalyst comprising a rhenium-containingmultimetallic catalyst.

[0013] In a second aspect, the invention provides a composition ofmatter comprising: a solid rhenium-containing multimetallic catalyst;water, hydrogen; and a 6 carbon sugar, a 6 carbon sugar alcohol orglycerol.

[0014] In another aspect, the invention provides a method of improvingthe catalytic activity or selectivity of a supported metal catalyst forthe reaction of hydrogen with a 6-carbon sugar, a 6-carbon sugaralcohol, or glycerol. In this method, rhenium is incorporated in a metalcatalyst to form a rhenium-containing multimetallic metal catalyst. TheRe-containing catalyst is reduced prior to, or simultaneous with ahydrogenolysis reaction. Preferably, the reduction is carried out byexposing the catalyst to hydrogen gas. Preferably, the 6-carbon sugar ora 6-carbon sugar alcohol is exposed to hydrogen and a rhenium-containingmultimetallic metal catalyst under conditions sufficient to convert atleast 40% of the sugar or sugar alcohol to propylene glycol, glycerol,ethylene glycol or any combination thereof. Here, “improving” means thatat the same conditions where the rhenium-containing multimetalliccatalyst results in 80% conversion, the yield of propylene glycol (“PG”)is improved by at least 5%, as compared with running the same reactionover each of: the same catalyst without rhenium, the same catalystwithout rhenium but containing added weight of metal equal to the weightof rhenium in the improved method, and the same catalyst without rheniumbut containing added moles of metal equal to the moles of rhenium in theimproved method.

[0015] In yet another aspect, the invention provides a method ofimproving the reaction of hydrogen with a 6 carbon sugar or a 6 carbonsugar alcohol. In this method, the 6 carbon sugar, or a 6 carbon sugaralcohol is exposed to hydrogen and a rhenium-containing multimetallicmetal catalyst under conditions sufficient to convert at least 40% ofthe sugar or sugar alcohol to propylene glycol, glycerol, ethyleneglycol or any combination thereof. In this method, “improving” meansthat when tested with a 20 weight % glycerol in aqueous solution with 2weight % sodium hydroxide, 1200 psi (8.2 MPa) hydrogen in a batchreactor for four hours, the yield of PG is improved by at least 5%, ascompared with running the same reaction over each of: the same catalystwithout rhenium, the same catalyst without rhenium but containing addedweight of metal equal to the weight of rhenium in the improved method,and the same catalyst without rhenium but containing added moles ofmetal equal to the moles of rhenium in the improved method.

[0016] In another aspect, the invention provides a hydrogenolysis methodin which a 5 carbon sugar, a 5 carbon sugar alcohol, lactate or lacticacid is reacted with hydrogen, at a temperature of at least 120° C., andin the presence of a solid rhenium-containing multimetallic catalyst.

[0017] In yet a further aspect, the invention provides a composition ofmatter comprising: a solid rhenium-containing multimetallic catalyst,water, hydrogen, and a 5 carbon sugar, a 5 carbon sugar alcohol; lactateor lactic acid.

[0018] In another aspect, the invention provides a method of makingpropylene glycol, comprising: reacting a composition comprising lactateor lactic acid with hydrogen in the presence of a catalyst; where acidis added to the composition prior to the step of reacting; where thelactate or lactic acid is converted with a yield of at least 60%; andwherein the PG selectivity is at least 80%.

[0019] In a further aspect, the invention provides a method of improvingthe reaction of hydrogen with a 5 carbon sugar, a 5 carbon sugaralcohol, lactate or lactic acid. In this method, a 5 carbon sugar, a 5carbon sugar alcohol, lactate and lactic acid is reacted with hydrogenin the presence of a solid, rhenium-containing multimetallic catalyst.In this method, “improving” means that at the same conditions where therhenium-containing multimetallic catalyst results in 80% conversion, theyield of PG is improved by at least 5%, as compared with running thesame reaction over any of: the same catalyst without rhenium, the samecatalyst without rhenium but containing added weight of metal equal tothe weight of rhenium in the improved method, and the same catalystwithout rhenium but containing added moles of metal equal to the molesof rhenium in the improved method.

[0020] In a further aspect, the invention provides method of improvingthe catalytic activity or selectivity of a supported metal catalyst forthe reaction of hydrogen with a 5-carbon sugar, or 5-carbon sugaralcohol, or lactic acid. The catalytic activity or selectivity of thesupported metal catalyst is improved by incorporating rhenium in saidmetal catalyst to form a rhenium-containing multimetallic metalcatalyst. The catalyst is typically reduced prior to or simultaneouswith the reaction of hydrogen with a 5-carbon sugar, or 5-carbon sugaralcohol, or lactic acid. Preferably, the method also includes the stepof exposing the sugar, sugar alcohol, or lactic acid to therhenium-containing multimetallic metal catalyst under conditionssufficient to convert at least 40% of the sugar, sugar alcohol or lacticacid to propylene, glycerol, ethylene glycol or any 1 combinationthereof. In this method, “improving” means that when tested with 20weight % xylitol in aqueous solution with 1 weight % sodium hydroxide,1200 psi (8.2 MPa) hydrogen in a batch reactor until there is 80%xylitol conversion, the yield of PG is improved by at least 5%, ascompared with running the same reaction over each of: the same catalystwithout rhenium, the same catalyst without rhenium but containing addedweight of metal equal to the weight of rhenium in the improved method,and the same catalyst without rhenium but containing added moles ofmetal equal to the moles of rhenium in the improved method.

[0021] The invention also includes methods of making 1, 3 propanediol byreaction of the starting materials described herein with hydrogen overRe-containing catalysts.

[0022] The invention includes any of the above aspects alone or incombination with any of the details in the following Examples anddescriptions of preferred embodiments.

[0023] Various embodiments of the inventive methods have been found toprovide numerous unexpected results that are superior over priortechnologies, including: stability of the catalytic system, highconversions at relatively mild conditions, desired selectivities, highvalue product distributions such as high concentrations of propyleneglycol, high PG selectivity at elevated temperature, production of 1, 3propanediol, and process control to produce desired products.

[0024] The product mixtures that can be derived from the inventivemethods offer advantages such as economy and environmentally-friendlyderivation from fermented materials. These product mixtures can be usedin various applications, for example, as anti-freeze.

[0025] The subject matter of the present invention is particularlypointed out and distinctly claimed in the concluding portion of thisspecification. However, both the organization and method of operation,together with further advantages and objects thereof, may best beunderstood by reference to the following description taken in connectionwith accompanying drawings wherein like reference characters refer tolike elements.

Glossary of Terms

[0026] “Rhenium-containing” means that a solid catalyst contains atleast 0.5 weight % Re, or that the catalyst contains a sufficient amountof rhenium such that when tested by hydrogenating a solution of 20 wt %sorbitol so that about 80% of the sorbitol is converted to shortercarbon chain products, the selectivity of the catalyst toward producingpropylene glycol increases by at least 5% (where increases by 5% refersto absolute improvement, for example the propylene glycol selectivityincreases from 20 to 25%.

[0027] “Multimetallic” means that the catalyst contains at least twometals (not including metals in the oxide support such as aluminum inalumina). In preferred embodiments, these metals function together toexhibit synergistic effects.

[0028] Carbon Molar Selectivity means the percent of carbon in aconverted starting material (such as a converted sugar alcohol) that isthe form of the selected species. For example, where a solutionoriginally contains 1 mole sorbitol (i.e., 6 mole carbon as sorbitol),and the product contains 0.5 mole sorbitol and 0.25 mole PG (i.e., 0.75mole carbon as PG), the PG carbon molar selectivity is 25%. In thiscase, the yield of PG is 12.5%. Unless indicated otherwise, the term“selectivity” in the present descriptions refers to carbon molarselectivity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 illustrates various pathways for the hydrogenolysis ofsorbitol and related compounds.

[0030]FIG. 2 is a plot of conversion vs. reaction time for glycerolhydrogenation over four catalysts.

[0031]FIG. 3 is a plot of conversion vs. reaction temperature forglycerol hydrogenation over a Ni/Re catalyst at varying pH and flowrate.

[0032]FIG. 4 is a plot of selectivity for glycerol hydrogenation overfour catalysts at various reaction times.

[0033]FIG. 5 is a plot of selectivity vs. temperature for glycerolhydrogenation over a Ni/Re catalyst at varying pH and flowrate.

[0034]FIG. 6 is a plot of conversion vs. temperature for sorbitolhydrogenolysis over a Ni/Re catalyst at varying pH and flowrate, and acomparison with a Ru catalyst.

[0035]FIG. 7 is a plot of PG selectivity vs. temperature for sorbitolhydrogenolysis over a Ni/Re catalyst at varying pH and flowrate, and acomparison with a Ru catalyst.

[0036]FIG. 8 is a plot of glycerol selectivity vs. temperature forsorbitol hydrogenolysis over a Ni/Re catalyst at varying pH andflowrate, and a comparison with a Ru catalyst.

[0037]FIG. 9 is a plot of conversion vs. temperature for xylitolhydrogenolysis over four catalysts.

[0038]FIG. 10 is a plot of selectivities vs. temperature for xylitolhydrogenolysis over five catalysts at 200° C.

[0039]FIG. 11 is a plot of PG selectivity vs. temperature for lacticacid hydrogenation at varying pH, hydrogen pressure, hydrogen-to-lacticacid ratio, and flowrate.

[0040]FIG. 12 is a plot of PG selectivity vs. temperature for lacticacid hydrogenation at varying pH, hydrogen pressure, hydrogen-to-lacticacid ratio, and flowrate.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0041] Feedstocks useful in the present invention contain at least oneof a sugar, sugar alcohol, glycerol, lactate or lactic acid. Preferredsugars include the sugars containing 6 carbon chains, such as glucose,galactose, maltose, lactose, sucrose, allose, altrose, mannose, gulose,idose, and talose (referred to herein as “6-carbon sugars”). Anotherpreferred group of sugars are the sugars containing 5 carbon chains,such as ribose, arabinose, xylose, and lyxose (referred to herein as“5-carbon sugars”). It should be understood that under some reactionconditions, especially basic conditions, it is believed that somesalt-like interactions may be formed with oxy moieties on the sugars orsugar alcohols and these species, if present, should be included withinthese definitions.

[0042] The feedstocks may be pure materials, purified mixtures or rawmaterials such as fermentation broth. Some feedstocks are commerciallyavailable. Some feedstocks could be obtained as side-products of otherprocesses such as corn processing. Indeed, another advantage of thepresent invention is that, in some embodiments, the process can usematerials that would otherwise be disposed as waste. The feedstocks canalso be intermediates that are formed as part of a larger process or inthe same process (such as sugar alcohols produced in the initial stageof hydrogenating a sugar). For some bio-based materials, it may bedesirable to filter the materials and/or pass them through an ionexchange column or columns.

[0043] In preferred embodiments, the feedstocks include water or anonaqueous solvent. Preferred nonaqueous solvents include methanol,ethanol, ethylene glycol, propylene glycol, n-propanol and i-propanol.Water is especially preferred because of its nontoxicity and prevalencein fermentation processes. The inventive processes have broadapplicability, and, in some less-preferred embodiments, the feedstockmay include proteins and other materials. Preferably, feedstocks contain20 to 50 wt % of reactants with the balance substantially composed ofsolvent.

[0044] Catalysts for the hydrogenolysis processes are metal-containingsolid catalysts. Preferably the catalysts include a high surface areasupport material that is selected to resist degradation under theintended reaction conditions. Such support materials are known in theart and may include high surface area oxide supports. Carbon, zirconiaand titania (especially in the rutile form) are especially preferredbecause of their stability in hydrothermal conditions (aqueous solutionsat above 100° C. and 1 atmosphere pressure). Supports can also be formedof mixed or layered materials, for example, in some preferredembodiments the support is carbon with a surface layer of zirconia orzirconia mixed with catalyst metals.

[0045] For hydrogenolysis reactions, the catalyst preferably containsrhenium. Based on its improvement with all metals tested thus far, it isbelieved that addition of rhenium will improve the hydrogenolysisperformance of any suitable hydrogenation catalyst. In preferredembodiments, the catalyst contains at least one other metal in additionto rhenium. Preferred additional metals include: Ni, Pd, Ru, Co, Ag, Au,Rh, Pt, Ir, Os and Cu, of which Ni, Pd and Ru are especially preferred,for example, Ni/Re, Pd/Re, and Ru/Re. In some embodiments, the mostpreferred additional metal is nickel.

[0046] Preferably, the catalyst contains 0.1 to 5 weight % Re, morepreferably 0.5 to 2.5 weight % Re, and still more preferably 0.5 to 1weight % Re. Also preferably, the catalyst contains 1 to 10 weight % ofadditional metals, more preferably 2 to 7 weight % additional metals,and still more preferably 2.5 to 5 weight % additional metals. Theseranges preferably occur together, for example, 0.5 to 1 weight % Re and2.5 to 5 weight % additional metals. The foregoing ranges of additionalmetals are based on experience with Ni and are believed to beappropriate for other metals; however, other metals may have differentpreferred ranges.

[0047] Without intending to limit the scope of the invention, it isbelieved that the rhenium acts as an oxygen acceptor. The rhenium mayalso facilitate dispersion and stablilization of the additional metal.It is an important discovery of the present invention that the rheniumand additional metal exhibit synergistic effects. That is, the effectson the catalytic activity and reaction performance are more than couldbe expected based on the performance of either metal acting alone.

[0048] Catalysts are preferably made by incipient wetness impregnationtechniques. A porous support may be purchased or prepared by knownmethods. A catalytic metal precursor is prepared or obtained. Theprecursor may be prepared, for example, by dissolving a metal compoundin water or acid or purchasing a precursor in solution. The precursormay be in the form of a cation or an anion. A typical precursor fornickel may be nickel nitrate dissolved in water. A typical precursor forruthenium may be ruthenium chloride. A typical precursor for rhenium maybe perrhenic acid. Each of the precursor materials may be in liquid orsolid form; these particles may also contain other components such ashalides, cations, anions etc. In some preferred embodiments, organicsolvents are avoided and the precursor impregnation solution is preparedonly in water. Conditions for preparing precursor solution will dependon the type of metal and available ligands. In the case of a particulatesupport, such as activated carbon powders, the support and precursorcomposition can be mixed in a suspension. The porous support ispreferably not coated by a vapor-deposited layer, more preferably themethod of making the catalyst does not have any vapor deposition step. Acatalyst metal can be deposited subsequent to, or simultaneous with, thedeposition of a metal oxide. Catalyst metal components can beimpregnated into the support in a single-step, or by multi-stepimpregnation processes. In a preferred method, the precursor for thecatalyst component is prepared in a single solution that is equivalentin volume to the measured amount of solvent that the porous support willuptake to exactly fill all of the pore volume. This solution is added tothe dry support such that it is absorbed by the support and fills all ofthe available pore volume. The support can then be vacuum dried in orderto remove the solvent and leave the catalytic metal precursor to coatthe surface of the support. Subsequent reduction will reduce thecatalytic material to its metallic state or another oxidation state andwill often disassociate the metal from its anion or cation used to makethe metal soluble. In most cases, the catalyst is reduced prior to use.

[0049] In methods of the present invention, hydrogenolysis of sugars andsugar alcohols preferably occurs in a temperature range of 140 to 250°C., more preferably 170 to 220° C. The hydrogenolysis reaction should beconducted under basic conditions, preferably at a pH of 8 to 13, morepreferably 10 to 12. Acids, particularly lactic acid, may form duringhydrogenolysis and neutralize some of the base. As the reactionprogresses, pH approaches neutral and PG selectivity decreases. Toameliorate this problem, additional base can be added to increase pH.

[0050] In flow reactors, the hydrogenolysis reaction is preferablyconducted at a weight hourly space velocity (WHSV) of 0.3 to 3 kgreactant per kg catalyst per hour. In batch to reactors, hydrogenolysisreaction times preferably range from 0.3 to 10 hours.

[0051] It has also been discovered that the yield of PG can be improvedby neutralizing or acidifying the product mixture resulting fromhydrogenolysis and hydrogenating the product mixture under neutral oracidic conditions. Because the hydrogenolysis is typically conducted inbasic conditions, the product mixture contains lactate salts. In somepreferred embodiments, solution containing lactate salts is passedthrough a cation exchange column to produce lactic acid which issubsequently hydrogenated. While reaction with lactates and/or lacticacid has been described with regard to products of hydrogenolysisreactions, it should be appreciated that the descriptions are equallyapplicable to lactates or lactic acid from any source. The lactic acidhydrogenation reaction can be conducted utilizing any suitablehydrogenation catalyst, but preferably contains at least one of Ru, Pt,Pd, Ir, and Rh; and more preferably, the rhenium-containing catalystsdescribed above.

[0052] Hydrogenation of lactic acid preferably occurs in a temperaturerange of 110 to 200° C., more preferably 140 to 170° C. Thehydrogenation of lactic acid should be conducted under neutral or acidconditions, preferably at a pH of 1 to 6, more preferably 3 to 5.

[0053] In flow reactors, the lactic acid hydrogenation reaction ispreferably conducted at a weight hourly space velocity (WHSV) of 0.3 to3 kg reactant per kg catalyst per hour. In batch reactors, lactic acidhydrogenation reaction times preferably range from 0.3 to 10 hours.

[0054] In another aspect of the invention, glycerol is hydrogenated toPG. In some preferred embodiments, glycerol is separated (or PG and/orother hydrogenolysis products are removed) from a product mixture suchas from sugar alcohol hydrogenolysis, and the resultingglycerol-enhanced (i.e., glycerol in a higher relative proportion thanin the initial product mixture) composition subjected to hydrogenationin the presence of a rhenium-containing catalyst as described above.Preferred reaction conditions are the same as those described for sugarsor sugar alcohols, although the glycerol to PG reaction can be operatedover a higher temperature range while still maintaining goodselectivity.

[0055] The hydrogenation/hydrogenolysis reactions can occur in anyreactor suitable for use under the desired conditions of temperature,pressure, and solvent. Examples of suitable apparatus include: tricklebed, bubble column reactors, and continuous stirred tank. Variousadditional components such as cation exchange columns, distillationcolumns, etc. are known to skilled workers and can be used in variousembodiments of the present invention.

[0056] The inventive compositions and catalytic methods can also becharacterized by their properties. Preferably, sugars and sugar alcoholsare greater than 50% converted, more preferably greater than 80%converted, and still more preferably greater than 90% converted.Preferably, these conversion rates co-occur with other characteristicsof the inventive compositions and catalytic methods. Preferred carbonmolar selectivity (“selectivity”) of sugar or sugar alcohols to PG is atleast 20%, more preferably at least 30%, and in some embodiments in therange of 25 to about 40%. Selectivity of sugar or sugar alcohols toglycerol is at least 20%, more preferably at least 25%, and in someembodiments in the range of 20 to about 32%. Selectivity of the sum ofPG, EG and glycerol is preferably at least 60%, more preferably at least75%, and in some embodiments in the range of 70 to about 90%.

[0057] Various embodiments of the present invention are characterized bynumerous surprisingly superior results including: enhanced selectivityto PG from sugar alcohols or glycerol; better PG yield from lactic acidwith high hydrogen pressure; and enhanced PG yield by converting lactateto lactic acid.

EXAMPLES Preparation Of Nickel/Rhenium on Carbon Catalyst

[0058] The carbon used for this preparation was a Calgon 120% CTCcoconut carbon. Incipient wetness for the carbon was measured at 0.85 ccof liquid per gram of carbon. Moisture content was determined to be1.3%.

[0059] The impregnation volume was calculated using the incipientwetness of 0.85 cc/g.

[0060] The total weight of catalytic metal required is calculated by thefollowing formula:

W _(mtl) =W _(c)*((1/P _(c))−1)

[0061] Where W_(c) is the weight of carbon being impregnated and P_(c)is the weight percent of carbon in the reduced catalyst mix, calculatedby taking 1 minus the weight percent of catalytic metal desired. In thecase of 2.5 wt % nickel/2.5 wt % rhenium catalyst the P_(c) value is0.95.

[0062] The weight of each of the catalytic metals (W_(Ni) and W_(Re)) isdetermined by multiplying the total weight of catalytic metal by thefraction that each particular metal represents in the total catalyticmetal weight. Thus:

W _(Ni) =W _(mtl)*(P _(Ni) /P _(Ni) +P _(Re))

W _(Re) =W _(mtl)*(P _(Re) /P _(Ni) +P _(Re))

[0063] Where P_(Ni) and P_(Re) are the weight percents of nickel andrhenium respectively in the reduced catalyst. In the case of 2.5 wt %nickel/2.5 wt % rhenium catalyst the P_(Ni) and P_(Re) value are both0.025.

[0064] The nickel was added to the catalyst as nickel nitrate (NiNO₃)from laboratory stock chemicals. In this state, the nickel nitrate isabout 20.2% nickel by weight. Thus, the weight of the nickel nitraterequired (W_(NiNo3)) is calculated by:

W _(NiNO3) =W _(Ni)/0.392

[0065] The rhenium was added to the catalyst as perrhenic acid (HReO₄)from Alfa Aesar. In this state, perrhenic acid is about 54.5% rhenium byweight, although this can vary between 50% to 55% depending on thesupplier. Thus the weight perrhenic acid needed (W_(HReO4)) iscalculated by:

W _(HReO4) =W _(Re)/0.545

[0066] Approximately 1.5 times the weight of water was added to thenickel nitrate in order to dissolve the material. This is approximate,and designed just to dissolve the nickel nitrate. To this mixture, thecalculated amount of perrhenic acid was added to the solution. Thesolution was added dropwise to the carbon adding about 10% of thesolution at a time. Between additions, the carbon is shaken thoroughly.Care should be taken to add the solution slowly, as the first additionsto the bare carbon heat up very quickly and may boil on the surface ofthe carbon.

[0067] After the entirety of the impregnation solution has been added,the vessel should be capped and let sit (with intermittent shaking) fora minimum of 15 minutes for smaller batches (5 g) and at least 30minutes for larger batches. After sitting, the vessel was placeduncapped into a vacuum oven and heated to 80C. and held at about 20 inHg(510 mmHg) vacuum. The catalyst should be held at these conditions for18 hours, or untie dry.

[0068] Upon removing the vessel from the vacuum oven, it was capped andallowed to cool. The catalyst was reduced before using.

[0069] Glycerol and Sorbitol Testing Examples

[0070] Glycerol Batch Reactor

[0071] 16.57 g of Calgon 120% CTC Coconut Carbon (16×40 mesh) wereplaced into a jar. This carbon was determined to have an incipientwetness value of approximately 0.9 cc/g for uptake of water. In agraduated cylinder, 4.57 g of nickel nitrate was measured. To thiscylinder, 1.71 g of perrhenic acid was added and then topped up to 15.0ml with deionized water. The mixture was then allowed to sit for about 5minutes. The solution was then added to the weighed carbon by pipette in1 ml increments. After each 1 ml aliquot, the carbon jar was capped,shaken, and thoroughly mixed. Upon addition of the entire 15.0 ml ofsolution, the carbon was sticky and slightly clumped, partially adheringto the inside of the jar. The loaded carbon was allowed to sit for 20minutes, with intermittent shaking. The jar was placed, uncapped, in avacuum oven set to 100° C. and −20 inHg and left to dry overnight. Thejar was then capped and cooled.

[0072] 2.5 g of the dried catalyst was then loaded into a 300 ccsemi-batch Parr reactor, which was then purged with nitrogen at roomtemperature. The reactor was filled to 500 psi (3.45 MPa) of hydrogen.The reactor was slowly stirred and brought up to 280° C. and held for 16hours. The reactor was then cooled, the gas removed, and 106.1 g of asolution of 25% glycerol and 0.5% sodium hydroxide in water added. 600psi (4.14 MPa) of hydrogen was put into the reactor and the heat turnedon. After 19 minutes, when the reactor reached 230° C., the pressure wasraised to 1300 psi (9.0 MPa) by adding hydrogen and held at an averagepressure of 1200 psi (8.2 MPa) by adding hydrogen to the reactor toraise it to 1300 psi (9.0 MPa) whenever it dipped to 1100 psi (7.6 MPa).The test was held at temperature for 4 hours and samples were pushed outintermittently through a valved dip tube.

[0073] HPLC analysis of the products is shown in the following tables.All selectivity data is shown in carbon molar selectivity. The prefix“Eng” means that the catalyst support was obtained from Engelhard, andthe suffix, such as “95” refers to the CTC value of the support providedby the manufacturer. TABLE 1 Batch Glycerol Hydrogenation as a Functionof Time at 230° C. Selectivity To hour Conversion PG EG Lactate 1 25.372.3 16.4 14.8 2 37.2 64.8 15.0 10.3 4 62.4 66.3 13.4 5.1

[0074] Conversion and selectivity over four different catalysts as afunction of time is shown in FIGS. 2 and 3. TABLE 2 Glycerol BatchHydrogenation - Conversion and Selectivity at 4 Hr, 230° C. Carbon Molar4 hr sample, 230 C. Ni/Re Re/Ni Ni Re Pressure Selectivity To: RunCatalyst ratio ratio wt % wt % MPa Conv. Lactate EG PG Gly-54 2% Ni/0.4%Re 5.0 0.2 2 0.4 4.14 36 19 12 42 Gly-46 2% Ni/0.4% Re 5.0 0.2 2 0.44.14 39 16 9 60 Gly-45 2% Ni/0.4% Re 5.0 0.2 2 0.4 12.41 61 8 9 88Gly-55 2% Ni/0.4% Re 5.0 0.2 2 0.4 12.41 60 10 13 78 Gly-48 2% Ni/0.67%Re 3.0 0.34 2 0.67 8.27 51 12 12 76 Gly-43 2% Ni/1.33% Re 1.5 0.67 21.33 4.14 58 9 10 58 Gly-44 2% Ni/1.33% Re 1.5 0.67 2 1.33 12.41 50 1312 68 Gly-39 5% Ni/1% Re 5.0 0.2 5 1 8.27 50 10 11 67 Gly-40 5% Ni/1% Re5.0 0.2 5 1 8.27 44 9 9 64 Gly-50 5% Ni/1.67% Re 3.0 0.33 5 1.67 12.4153 13 13 76 Gly-47 5% Ni/3.33% Re 1.5 0.67 5 3.33 4.14 68 9 18 53 Gly-517% Ni/1% Re 7.0 0.14 7 1 4.14 49 16 12 62 Gly-38 7% Ni/1% Re 7.0 0.14 71 8.27 48 9 9 64 Gly-49 7% Ni/1% Re 7.0 0.14 7 1 12.41 53 10 11 79Gly-56 7% Ni/1% Re 7.0 0.14 7 1 12.41 56 12 13 75 Gly-41 7% Ni/1.4% Re5.0 0.2 7 1.4 4.14 70 8 10 54 Gly-36 7% Ni/1.4% Re 5.0 0.2 7 1.4 8.27 4811 12 63 Gly-42 7% Ni/1.4% Re 5.0 0.2 7 1.4 12.41 45 11 12 58 Gly-57 7%Ni/1.4% Re 5.0 0.2 7 1.4 12.41 55 12 13 68 Gly-37 7% Ni/2.25% Re 3.10.32 7 2.25 8.27 55 9 13 60

[0075] TABLE 3 Glycerol Batch Hydrogenation Over Various CatalystsGlycerol Hydrogenolysis At 4 Hours Catalyst Conv PG Sel Lactic Sel EGSel Temp (C) Base (%) glass liner 3% Ag, Eng 95 10.2 39.3 31.2 7.0 2504.1 yes 3% Re, Eng 95 6.3 48.3 10.4 3.8 200 4.1 yes 1.5% Cu/1.5% Re,CCC120 9.5 45.9 5.3 4.5 200 4.1 yes 1.5% Ag/1.5% Re, CCC120 5.9 49.5 8.54.1 200 4.1 yes 5% Ni/5% Re, Eng 121 41.2 63.2 20.1 9.3 200 4.1 yes 1.5%Ag/1.5% Re, CCC120 8.0 59.2 14.0 5.5 200 4.1 no 5% Ni, Eng 74 2.6 88.511.1 4.6 200 1 no 3% Ni 3% Cu, CCC120 7.0 84.0 10.8 6.1 200 1 no 3%Cu/3% Re, CCC120 12.3 76.6 8.5 2.0 200 1 no 3% Ni/3% Re, CCC120 13.863.8 15.1 14.9 200 1 no 9% Rh/9% Re, Eng 121 14.7 70.1 2.7 14.4 150 1 no3% Ni/3% Re, CCC120 25.8 66.9 13.5 11.2 200 2 no

[0076] TABLE 4 Glycerol Batch Hydrogenation Over Various CatalystsGlycerol Hydrogenolysis Base Catalyst Conv. PG 1,3-PD Lactic EG Temp (%)5% Ni/5% Re, CCC120 62.4 66.3 0.0 5.1 13.4 230 2 5% Ni/5% Re, Eng 9549.7 58.9 0.0 7.8 15.1 230 2 2.5% Pd/5% Re, Eng 95 49.1 50.6 0.0 7.4 5.1230 2 5% Pd/5% Re, Eng 95 48.9 55.2 0.0 7.2 6.0 230 2 2.5% Ni/2.5% Re,CCC120 47.3 44.3 4.6 0.0 13.0 230 0 5% Ni/5% Re, Eng 95 47.1 52.7 0.03.2 17.6 230 1 5% Ni/5% Re, Eng 95 46.9 53.3 0.0 0.4 19.5 230 0 5% Pd/5%Re, Eng 95 41.0 48.3 0.0 4.2 5.4 230 1 5% Pd/5% Re, Eng 95 38.9 46.8 0.00.4 5.4 230 0 2.5% Ni/2.5% Re, Eng 95 38.4 54.0 2.4 2.0 14.3 230 0 2.5%Pd/2.5% Re, CCC120 25.5 50.6 5.2 0.0 5.8 230 0 5% Ni, Eng 95 15.7 56.00.0 19.2 6.1 230 2 5% Re, Eng 95 13.7 40.2 0.0 20.6 4.2 230 2

[0077] There were many unexpected results from the glycerolhydrogenolysis. As can be seen from the data, the selectivity to lactatedecreases substantially with increasing time. Conversion and selectivitydepend on both the type of catalyst and hydrogen pressure. Re-containingmultimetallic catalysts resulted in substantially better PG selectivityand conversion. The performance of the Ni-Re catalysts was especiallygood. Increased hydrogen pressure was unexpectedly discovered to resultin enhanced PG selectivity. Also, where base was not added to theglycerol feedstock, 1,3-propanediol was unexpectedly found to beproduced from the hydrogenolysis of glycerol.

[0078] In some preferred embodiments, the conversion of glycerol to PGis conducted as a separate step from the hydrogenolysis of a sugaralcohol. In this two step (or multi-step) process, glycerol resultingfrom the hydrogenolysis of a sugar alcohol is isolated or its relativeconcentration increased (for example by removing at least a portion ofthe PG, or other product, produced). In some preferred embodiments,glycerol is present at a higher concentration than the sum of PG, EG andsugar alcohol.

[0079] Glycerol Flow Reactor Example

[0080] 13.37 g of 120% CTC Calgon Coconut Carbon (“CCC,” 16×40 Mesh) wasplaced into ajar. To a graduated cylinder containing 1.7402 of NickelNitrate was added. 0.6974 g of perrhenic acid and then topped up to 11.5ml with deionized water. This solution was then added to the weighedcarbon by pipette in 1.0 ml increments. After each 1.0 ml aliquot, thecarbon was shaken, and thoroughly mixed. Upon addition of the entire11.5 ml of solution, the carbon was sticky and slightly clumped,partially adhering to the inside of the jar. The loaded carbon wasallowed to sit for 45 minutes, with intermittent shaking. The carbonappeared mostly dry and granular, with some material still adhering tothe inside of the jar. The jar was placed, uncapped, in a vacuum ovenset to 100° C. and −20 inHg and left to dry overnight. The jar was thencapped and cooled. The catalyst was designated as a 2.5% nickel/2.5%rhenium catalyst.

[0081] 11.4 g of this dried catalyst was placed in a downflowtrickle-bed reactor and packed to constitute a 30 cc bed. Hydrogen waspassed slowly across the bed at atmospheric pressure, and the bed washeated to 120° C. and held for 18 hours. The temperature was raised to280° C. and held for 4 hours. The reactor was then cooled underhydrogen.

[0082] The reactor was then raised to 1200 psi and 160° C., and a largeset of reaction conditions were tested for converting a glycerolfeedstock to propylene glycol. This was accomplished by processing a 10%glycerol (by weight) feedstock at a hydrogen excess of 5 to 1 at fullreaction, while varying temperatures from 160° C. to 240° C., pressuresbetween 800 psi and 1600 psi, base concentrations between 0 and 1% (byweight of feedstock), and flowrates between 15 and 200 ml/hr.

[0083] Selected data for the glycerol hydrogenation over a 2.5% Ni/2.5%Re/C catalyst in a flow reactor is summarized in FIGS. 4 and 5. Theamount of NaOH is indicated in units of wt % NaOH in the solution. Thepresence of base was unexpectedly found to substantially increase theconversion rate and selectivity to PG. The reasons for effect is notknown, but it could be that base enhances the wetting of catalyst. Inpreferred embodiments, the molar ratio of base/glycerol is at least0.05, more preferably in the range of 0.1 to 1.0, and still morepreferably 0.1 to 0.5; or, in another preferred embodiment, the solutionis between 0.25 and 5 weight % base. Preferably, the reaction is run ata pressure in the range of 600 to 1800 psi (4 to 12 MPa) hydrogen.Temperature of the glycerol hydrogenation is preferably in the range of170 to 250° C., more preferably 200 to 230° C. Glycerol conversion ispreferably at least 80% , more preferably at least 90% , and in someembodiments 80-97% . PG selectivity is preferably at least 50% , morepreferably at least 60% , and in some embodiments 60 to about 80% .

[0084] Sorbitol Flow Reactor Examples

[0085] These examples used the same bed as was used for the glycerolflow reactor testing. Following the glycerol conversion testing, thereactor was used to examine the conversion of sorbitol over the Ni/Recatalyst. The reactor was heated and pressurized with hydrogen to 1200psi (8.3 MPa) and 200° C., and a number of reaction conditions weretested for converting the sorbitol feedstock to PG, EG, and glycerol.This was accomplished by processing a 25% sorbitol (by weight) feedstockat a hydrogen excess of 5 to 1 at full reaction, while varying thetemperatures between 180° C. and 240° C., pressures between 1200 psi(8.3 MPa) and 1800 psi (12.4 MPa), base concentrations between 0.5 and1.5% (by weight), and flowrates between 15 and 75 ml/hr. The run wascompared against a previous flow reactor experiment using a 2.5%ruthenium catalyst and equivalent flowrate and bed volume combination. Aportion of the results are summarized in the FIGS. 6-8.

[0086] From the data it can be observed that the Ni/Re catalystexhibited good selectivity to PG while at the same time providingsuperior conversion rates as compared to a Ru catalyst.

[0087] Sorbitol Batch Reactor Example

[0088] 5.09 g of Calgon 120% CTC Coconut Carbon was placed into ajar. Toa graduated cylinder containing 0.6728 of Nickel Nitrate was added0.2525 g of perrhenic acid and then topped up to 4.4 ml with deionizedwater. The mixture was then allowed to sit for about 5 minutes. Thesolution was then added to the weighed carbon by pipette in 0.5 mlincrements. After each 0.5 ml aliquot, the carbon was shaken, andthoroughly mixed. Upon addition of the entire 4.4 ml of solution, thecarbon was sticky and slightly lumped, partially adhering to the insideof the jar. The loaded carbon was allowed to sit or 30 minutes, withintermittent shaking. The carbon appeared mostly dry and granular, withsome material still adhering to the inside of the jar. The jar wasplaced, uncapped, in a vacuum oven set to 100° C. and −20 inHg (510mmHg) and left to dry overnight. The jar was then capped and cooled.

[0089] 2.53 g of the dried catalyst were then loaded into a 300 ccsemi-batch Parr reactor, which was then purged with nitrogen at roomtemperature. The reactor was filled with 3.5 MPa (500 psi) of hydrogen.The reactor was slowly stirred and brought up to 280° C. and held for 16hours. The reactor was then cooled, the gas removed, and 105.5 g of asolution of 25% sorbitol and 0.94% potassium hydroxide in water wasadded. 600 psi (4.1 MPa) hydrogen was put into the reactor and the heatwas turned on. After 20 minutes, when the reactor reached 220° C., thepressure was raised to 1200 psi (8.3 MPa) by adding hydrogen and thehydrogen intake valve was left open regulated to 1200 psi (8.3 MPa). Thetest was held at temperature for 4 hours and samples were pushed outintermittently through a valved dip tube.

[0090] Samples were analyzed via HPLC to yield the results shown in thetables below. The 0.0 hour value corresponds to the point at which thereactor reached operating temperature. Batch data in the tables wascollected in samples containing 0.94 wt. % KOH. As can be seen,selectivity to glycerol decreased with increasing reaction time due tocontinuing C—O hydrogenolysis. Although there appears to be variationsin the data, in general, it appears that improved hydrogen pressurecauses increased conversion. TABLE 5 Batch Sorbitol Hydrogenolysis as aFunction of Time hr Conv. xylitol erythritol unk-OH lactate glycerol1,2,4 BTO EG PG 2,3 BDO 1,3 BDO 1,2 BDO 0.0 17.1 5.1 1.8 3.2 5.2 22.90.0 13.2 29.4 3.7 0.0 2.5 1.0 37.9 8.3 3.2 3.6 6.9 20.2 1.6 10.7 18.81.9 0.0 1.4 2.0 42.6 10.7 3.6 4.0 8.1 21.5 2.2 11.4 20.8 1.5 0.8 1.5 4.056.3 9.6 2.7 2.9 5.6 17.4 2.3 10.1 20.9 2.4 0.0 2.5

[0091] TABLE 6 Batch Sorbitol Hydrogenolysis at 4 Hours at 220° C.Sorbitol Batch Data, 4 Hour Sample, 220 C. Ni Re Pressure Carbon MolarSelectivity to: Run wt % wt % MPa Conv xylitol erythritol threitollactate glycerol EG PG Sorb20 7 2.25 8.27 58.5 9 3 3 6 19 11 22 Sorb25 71.4 4.14 62.8 5 1 2 4  9  7 15 Sorb19 7 1.4 8.27 57.8 8 3 3 6 19 12 22Sorb26 7 1.4 12.41 48.8 7 2 3 6 16 10 19 Sorb47 7 1 4.14 39.3 0 5 0 1319 16 30 Sorb21 7 1 8.27 51.6 7 2 3 7 19 13 23 Sorb45 7 1 12.41 57.0 7 34 9 29 16 27 Sorb46 5 3.33 4.14 56.8 8 5 0 9 17 13 24 Sorb48 5 1.6712.41 58.8 8 3 4 10 26 15 24 Sorb22 5 1 8.27 55.3 7 3 3 6 20 12 23Sorb27 2 1.33 4.14 54.2 7 2 2 6 12 10 21 Sorb44 2 1.33 12.41 57.4 8 3 410 27 15 25 Sorb32 2 0.67 8.27 54.5 6 2 3 8 19 13 24 Sorb34 2 0.4 4.1444.2 7 2 3 10 15 14 29 Sorb35 2 0.4 12.41 55.7 4 2 2 5 20 15 31

[0092] Xylitol Flow Reactor Examples

[0093] The catalyst used for these examples was a 2.5% Ni/2.5% Re on120% CTC CCC support, prepared as described above. The flow reactor wasoperated as discussed above with a xylitol feed concentration of 20 wt.% and a hydrogen pressure of 12.4 MPa (1200 psi). Base % is the wt % ofKOH present in the feedstock.

[0094] Xylitol flow and batch data is reported in terms of weight %selectivity which is defined as the weight of a particular productcompound recovered (such as PG produced in this case) divided by theweight of the feedstock compound actually converted (such as xylitolconverted in this case). For example, if 100 grams of xylitol was fedinto a reactor as the feedstock, and 50 g of xylitol was converted to 30g of PG and 20 g of EG, then the weight % selectivity for PG would be 30g/50 g or 60 weight % selectivity. Likewise, the weight % selectivityfor the EG product would be 20 g/50 g or 40 weight % selectivity. TABLE7 Xylitol Flow Reactor Summary Temp (C) 140 160 160 160 160 160 170 170180 180 180 200 200 200 200 feed rate 25 100 100 50 50 50 50 25 100 5025 200 150 100 50 (ml/mn) Contact (hr) 1.4 0.35 0.35 0.7 0.7 0.7 0.7 1.40.35 0.7 1.4 0.175 0.233 0.35 0.7 Base % 1 1 0.25 1 0.25 0.1 1 1 1 1 1 11 1 1 Conversion 19.7 27.2 8.1 44.9 15.2 10.2 74.5 92.7 79.7 94.5 98.485.1 93.7 99.8 98.3 Weight Selectivity PG 10.2 13.5 8.5 16.8 8.8 6.721.9 26.1 25.9 28.1 30.3 29.8 30.8 29.5 30.8 Glycerol 22.3 21.0 22.523.2 21.6 20.2 16.9 13.6 17.1 11.3 8.6 9.7 8.2 8.7 7.4 EG 24.5 27.3 21.326.7 23.3 19.8 28.0 28.2 29.8 29.2 28.6 35.2 29.7 29.2 27.9 Lactate 32.724.5 37.1 20.9 33.8 35.2 11.0 6.4 8.4 5.0 3.5 4.3 3.8 3.9 3.7 Other 3.02.0 4.9 5.2 0.7 1.9 8.1 11.5 22.6 11.3 13.4 11.1 11.7 15.7 10.3

[0095] From this data can be seen the surprising results that, over aRe-containing catalyst, higher temperature, basic conditions and longercontact times improve conversion and selectivity to PG. PG yield couldbe increased further by acidifying the lactate by-product to lactic acidfollowed by hydrogenation to convert the lactic acid to PG.

[0096] Xylitol Batch Hydrogenolysis

[0097] Xylitol batch hydrogenolysis was conducted under conditions asdescribed above for sorbitol. Results are shown in FIGS. 9 and 10.Xylitol conversion was measured at 4 hours over the catalysts (left toright in FIG. 9) 2.5 wt. % Ni/2.5 wt. % Re/C, 2.5% Ru/C, 2.5% Rh/2.5%Re/C, 2.5% Pd/2.5% Re/C, and 2.5% Ru/0.5% Re/C The Ni/Re catalystresulted in surprisingly superior conversion. Furthermore, the Ni/Recatalyst demonstrated surprisingly superior selectivity to PG, EG andglycerol.

[0098] Arabinitol Batch Hydrogenolysis

[0099] Arabinitol was subjected to hydrogenolysis under conditionssimilar to the xylitol batch hydrolysis. Results are shown in Table 8below in weight % selectivities. Arabinitol-1 Conversion Data CatalystDescription: 2.5% Ni 2.5% Re/120% CTC (CCC) Carbon (Temp. = 200 C.; 1200PSIG) Arabitol EG Wt. % PG Wt. % Gly Wt. % Lac Wt. % EtOH Wt. % OtherWt. % EG + PG + Gly Sample # Conversion Selectivity SelectivitySelectivity Selectivity Selectivity Selectivity Selectivity 0.5 Hour55.90% 31.87% 20.61% 14.97% 12.05% 0.00% 3.30% 67.45% 1.0 Hour 75.00%31.44% 20.27% 14.52% 11.54% 0.00% 2.96% 66.23% 2.0 Hour 82.00% 31.24%20.29% 13.82% 11.68% 0.00% 2.73% 65.35% 3.0 Hour 83.90% 31.15% 20.43%13.16% 11.45% 0.00% 2.69% 64.74% 4.0 Hour 86.30% 31.07% 20.58% 12.82%11.23% 0.00% 2.66% 64.47%

[0100] Lactic Acid Hydrogenation

[0101] Lactic Acid Batch Hydrogenation

[0102] Catalyst testing was conducted in a semi-batch mode underconstant hydrogen pressure using a 300 cc, 316 SS Parr autoclave reactorsystem fitted with a Magnadrive stirrer and stirrer tachometer. 2.50 gof the 55794-107 pre-reduced catalyst sample was weighed into a cleanPyrex glass liner, then the liner and the contained catalyst were sealedinside the autoclave body. After pressure testing the assembled reactorsystem, 250 psi of pure hydrogen is charged to the reactor, the stirrermotor started and set to approximately 150 rpm then the reactor isheated up to 280° C. in order to re-reduce the catalyst prior tointroduction of the feeds. The temperature is maintained at 280° C. for4 hours, then is quickly cooled back to room temperature. After cooling,the reactor was flushed with nitrogen, then 103.8 g of a 19.7% lactatefeedstock solution (19.89% lactic acid in D.I.water) was added to thereactor liner, containing the catalyst, through the liquid samplingport. The vessel was then purged several times with pure hydrogen, thenre-pressurized to 1500 psi with hydrogen. The stirrer motor was turnedon and the stirrer speed adjusted to ˜500 rpm. The reactor was rapidlyheated to 150° C. and the gas inlet opened to maintain the hydrogenpressure within the vessel at a constant 2500 psi pressure. Liquidsamples are withdrawn from the vessel after 1, 2, and 4 hour intervals.The liquid samples are analyzed by high pressure liquid chromatographyto determine the concentrations of residual lactic acid, PG, andpropanols in the solutions. Lactic acid conversions and productselectivities for each product are then calculated. Table 9, below,shows data from the batch testing at 4 hours. TABLE 9 Lactic AcidHydrogenation Cat. Comp. Carbon Support Temp. (° C.) Press. (psi) Conv.PG SEL. PG Yield 2.5% Pd/2.5% Zr/C Calgon PCB 225° C. 1500 7.5% 19.1%1.4% 2.0% Pd/5% Zr/C Eng. 121% CTC 225° C. 1500 4.1% 28.3% 1.2% 2.5%Ru/10% Zr/C Eng. 121% CTC 200° C. 1500 88.5% 82.8% 73.3% 5% Ru/C Calgon120% CTC 200° C. 1500 93.7% 66.4% 62.2% 2.5% Ru/C Calgon PCB 200° C.1500 76.4% 82.8% 63.3% 2.5% Ru/10% Zr/C Calgon 120% CTC 200° C. 150083.5% 87.0% 72.7% 5% Ru/ZrO₂ Eng. Zirconia 200° C. 1500 52.3% 95.4%49.9% 2.5% Ru/C Calgon 120% CTC 200° C. 1500 93.3% 74.9% 69.8% 2.5%Ru/10% Zr/C Calgon PCB 200° C. 1500 81.3% 76.0% 61.8% 2.5% Ru/5% Zr/CCalgon 120% CTC 200° C. 1500 88.2% 70.7% 62.4% 2.5% Ru/5% Zr/C CalgonPCB 200° C. 1500 73.6% 74.6% 54.9% 2.5% Ru/10% Zr/C Calgon 130% CTC 200°C. 1700 89.5% 78.7% 70.4% 2.0% Ru/C Calgon 120% CTC 200° C. 1700 94.2%71.4% 67.2% 2.5% Ru/C Calgon 120% CTC 180° C. 1700 92.9% 83.8% 77.8%2.5% R/C Calgon 120% CTC 180° C. 2450 96.6% 90.1% 87.1% 2.5% Ru/C Calgon120% CTC 160° C. 2450 86.5% 95.2% 82.4% 2.5% Ru/C Calgon 120% CTC 180°C. 2500 98.4% 93.2% 91.7% 2.5% Ru/5% Zr/C Calgon 120% CTC 200° C. 160092.6% 69.7% 64.5% 2.5% Ru/15% Zr/C Calgon 120% CTC 180° C. 2400 88.3%85.6% 75.6% 2.5% Ru/C Calgon PCB 180° C. 2400 84.9% 89.7% 76.2% 2.5%Ru/2.5% Re/C Calgon 120% CTC 150° C. 2500 95.8% 96.3% 92.3% 4.8% Ru/4.8%Re/C Calgon 120% CTC 180° C. 2500 98.6% 87.3% 86.1% 4.8% Ru/4.8% Re/CCalgon 120% CTC 160° C. 2500 95.0% 94.1% 89.4% 1.5% Ru/C Calgon 120% CTC180° C. 2500 93.9% 93.9% 88.1% 1.5% Ru/1.5% Re/C Calgon 120% CTC 150° C.2500 59.5% 100% 59.5% 1.5% Ru/1.5% Re/C Calgon 120% CTC 180° C. 250099.7% 86.0% 85.7% 1.5% Ru/1.5% Re/ Calgon 120% CTC 160° C. 2500 72.1%93.8% 67.6% 5% Zr/C 1% Ru/C Calgon 120% CTC 180° C. 2500 90.3% 90.3%81.6% 2.5% Ru/10% Zr/ Calgon 120% CTC 180° C. 2400 16.1% 100% 16.1% 1.0%Ru/5% Zr/C Calgon 120% CTC 180° C. 2400 74.9% 95.1% 71.3% 1.5% Ru/0.5%Re/C Calgon 120% CTC 160° C. 2350 92.0% 88.3% 81.3% 1.0% Ru/C Calgon120% CTC 160° C. 2350 70.3% 98.7% 69.3% 1.5% Ru/C Eng. 95% CTC 180° C.2400 89.2% 91.1% 81.2% 1.5% Ru/5% Zr/C Eng. 95% CTC 180° C. 2400 88.5%95.2% 84.3% 1.5% Ru/5% Zr/C Calgon 120% CTC 180° C. 2400 89.4% 88.9%79.5% Zr sol prep 1.5% Ru/5% Zr/C Calgon 120% CTC 160° C. 2430 67.9%93.7% 63.7% 1.5% Ru/C Calgon 120% CTC 160° C. 2400 87.0% 91.3% 79.5%1.5% Ru/5% Zr/C Calgon 120% CTC 160° C. 2400 81.1% 89.4% 72.6% 1.5% Ru/CCalgon 120% CTC 180° C. 2350 93.6% 88.9% 83.2% 1.5% Ru/2.5% Zr/C Calgon120% CTC 180° C. 2450 86.6% 96.4% 83.5% 2.5% Ru/2.5% Re/C Calgon 120%CTC 180° C. 2500 98.3% 76.4% 75.1% 2.5% Ru/2.5% Zr/C Calgon 120% CTC180° C. 2500 95.4% 81.6% 77.9% 1.5% Ru/1.5% Re/C Calgon 120% CTC 180° C.2500 99.4% 83.4% 82.9% 4.8% Ru/4.8% Zr/C Calgon 120% CTC 180° C. 250098.5% 84.7% 83.4% 2.5% Ru/2.5% Re/C Calgon 120% CTC 180° C. 2500 100%75.0% 75.0% 5% Ru/C Calgon 120% CTC 180° C. 2500 99.4% 77.2% 76.7% 3.5%Ru/C Calgon 120% CTC 180° C. 2500 98.7% 85.8% 84.7% 2.5% Ru/1.0% Zr/CCalgon 120% CTC 180° C. 2500 96.8% 90.5% 87.6% 3.5% Ru/1% Zr/C Calgon120% CTC 180° C. 2500 98.1% 82.6% 81.0% 2.5% Ru/2.6% Ti/C Calgon 120%CTC 180° C. 2500 94.8% 86.7% 82.2%

[0103] It was surprisingly discovered that the higher hydrogen pressureimproved conversion and selectivity to PG—this can be seen by comparinghydrogenation results run at 180° C. over Ru/C at 1700 psi (78% PGyield) versus 2450 psi (87% PG yield) and 2500 psi (92% PG yield).Excessive zirconia (which is coprecipitated with the metal onto thecarbon support) can reduce conversion efficiency.

[0104] Testing was also conducted in flow reactors of the conversion oflactic acid to PG. Testing conditions were similar to those describedabove for sorbitol except that pH was unadjusted when preparing thelactic acid feedstock resulting in an acidic solution representing thepH of lactic acid at the feedstock concentration. The hydrogenation oflactic acid is preferably conducted in neutral to acidic conditionssince it is believed that these conditions will avoid lactate formation.A sample of results of this testing is summarized in FIGS. 11-12. As canbe seen, in a flow reactor, conversion increases with temperature whileselectivity decreases. Under the flow reactor conditions tested, it wassurprisingly discovered that increasing hydrogen pressure increased bothyield and selectivity while increasing the excess of H₂ to lactic acidhad no significant effect on either conversion or selectivity. Pressureduring hydrogenation of lactic acid is preferably above 2100 psi (15MPa), more preferably above 2300 psi (16 MPa), and in some embodiments16-35 MPa. The higher pressure appears to reduce the over-reduction toethanol.

CLOSURE

[0105] While preferred embodiments of the present invention have beenshown and described, it will be apparent to those skilled in the artthat many changes and modifications may be made without departing fromthe invention in its broader aspects. The appended claims are thereforeintended to include all such changes and modifications as fall withinthe true spirit and scope of the invention.

We claim:
 1. A hydrogenolysis method comprising: reacting a compositionwith hydrogen, at a temperature of at least 120° C., and in the presenceof a solid catalyst; wherein the composition comprises a componentselected from the group consisting of: a 5 carbon sugar, a 5 carbonsugar alcohol, and lactic acid; and wherein the solid catalyst comprisesa rhenium-containing multimetallic catalyst.
 2. The method of claim 1wherein the carbon molar selectivity to PG is 25 to 40% .
 3. The methodof claim 1 wherein the method comprises a continuous conversion of a5-carbon sugar alcohol and the solid catalyst comprises rhenium andnickel.
 4. The method of claim 3 wherein the PG selectivity is at least30% .
 5. A composition of matter comprising: a solid rhenium-containingmultimetallic catalyst; water, hydrogen; and a 5 carbon sugar or a 5carbon sugar alcohol.
 6. The composition of claim 5 wherein the solidcatalyst comprises nickel and a carbon support.
 7. The composition ofclaim 6 wherein the water has a basic pH.
 8. The composition of claim 6wherein the catalyst contains 0.1 to 5 weight % rhenium and 1 to 10weight % nickel.
 9. The composition of claim 5 comprising 20 to 50weight % of said 5-carbon sugar or sugar alcohol; and wherein thecatalyst comprises nickel.
 10. A method of making propylene glycol,comprising: reacting a composition comprising lactate or lactic acidwith hydrogen in the presence of a catalyst; wherein acid is added tothe composition prior to the step of reacting; wherein the lactate orlactic acid is converted with a yield of at least 60% ; and wherein thePG selectivity is at least 80% .
 11. The method of claim 10 wherein thestep of reacting lactate or lactic acid comprises reacting with hydrogenat a pressure of at least 2300 psi (15.6 MPa) wherein the carbon molarselectivity to PG is at least 30% .
 12. A method of improving thereaction of hydrogen with a composition, comprising: exposing thecomposition to hydrogen in the presence of a solid, rhenium-containingmultimetallic catalyst; wherein the composition comprises a componentselected from the group consisting of: a 5 carbon sugar, a 5 carbonsugar alcohol, lactate and lactic acid; and converting at least 80% ofsaid component to lower molecular weight products including propyleneglycol (PG); wherein improving means that at the same conditions wherethe rhenium-containing multimetallic catalyst results in said at least80% conversion, the yield of PG is improved by at least 5% , as comparedwith running the same reaction over each of: the same catalyst withoutrhenium, the same catalyst without rhenium but containing added weightof metal equal to the weight of rhenium in the improved method, and thesame catalyst without rhenium but containing added moles of metal equalto the moles of rhenium in the improved method.
 13. The method of claim12 wherein the catalyst comprises nickel and the conversion of thecomponent is continuous.
 14. The method of claim 13 wherein the catalystcomprises a carbon support.
 15. The method of claim 14 wherein thecomponent comprises xylitol.
 16. The method of claim 13 wherein thecomponent comprises a 5 carbon sugar.
 17. The method of claim 1 whereinthe temperature is in the range of 170 to 220° C. and a pH of 8 to 13.18. The method of claim 17 wherein the component comprises a 5 carbonsugar or 5 carbon sugar alcohol in aqueous solution.
 19. The method ofclaim 18 wherein selectivity to the sum of PG, EG and glycerol is atleast 75% .